Method of making seamless tubing

Abstract

A process for producing seamless tubes of austenitic steels is disclosed. A metallic melt is continuously poured into a cooled mold having a round molding cavity. The as yet fully unsolidified extracted billet is electromagnetically agitated in a direction about its longitudinal axis. Once hardened, the billet is cross cut, and the castings are subjected to annealing at a temperature between 1100° C. and 1250° C. (preferably between 1150° C. and 1200° C.) for between 30 minutes and 4 hours (preferably between 1 hour and 2 hours). The castings are allowed to cool, are machined into extrusion blooms and the seamless tubes produced by extrusion of the blooms.

We claim: 
     
       1. In a process for producing seamless tubes of austenitic chromium-nickel steels by continuous casting, wherein a metallic melt is poured continuously into a cooled mold having a round molding cavity, said melt being allowed to solidify partially in said cavity, and wherein a billet is extracted from said mold and cut into crosscut lengths after thoroughly hardening, the improvement comprising electromagnetically agitating said billet in a direction about its longitudinal axis prior to complete hardening, when said billet comprises a billet shell and a liquid billet core, annealing said crosscut continuous castings at a temperature of from 1100° C. to 1250° C. for a holding time between 30 minutes and 4 hours, cooling said casting and thereafter mechanically reducing said castings to extrusion blooms by machining, and extruding said blooms, without hot-working said blooms, to produce said seamless tubes. 
     
     
       2. A process for producing seamless tubes according to claim 1, further comprising moving said metallic melt at least in a portion of said mold about the longitudinal axis of said billet while the relative motion between said billet shell and said liquid billet core extends as far as the casting surface in said mold. 
     
     
       3. A process for producing seamless tubes according to claims 1 or 2, further comprising annealing said continuous castings at a minimum temperature of approximately 700° C. at their surface immediately after casting. 
     
     
       4. A process for producing seamless tubes according to claims 1 or 2, further comprising mechanical reducing said billets into said extrusion blooms prior to annealing. 
     
     
       5. A process for producing seamless tubes according to claim 4, further comprising extruding said extrusion bloom as cast immediately from the annealing heat. 
     
     
       6. A process for producing seamless tubes in accordance with any of claims 1, 2, 4 or 5, wherein said annealing temperature is from 1150° C. to 1200° C., and said holding time is between 1 hour and 2 hours.